The prior art contains numerous examples of rotary type speed changing devices. Among these prior art examples are U.S. Pat. No. 2,884,815 to Pittman, Jr., which teaches a speech changer of the gear assembly type characterized in that the ratio of the input rotational speed to the output rotational speed is high and in which the number of stages of speed reduction can be changed by changing the axial length of the assembly; U.S. Pat. No. 3,529,480 to Kaspareck, which teaches an incremental or stepping drive that has a high torque capacity; U.S. Pat. No. 4,155,276 to Fengler, which teaches a two stage speed reducing transmission for use primarily in the gas turbine engine field to reduce the high rotational speed of the turbine rotor for other uses; U.S. Pat. No. 4,798,104 to Chen et al., which teaches a speed changer of the oscillatory tooth and needle gear transmitting type; and U.S. Pat. No. 4,841,81 1 to Bajulaz, which teaches a mechanical speed reducer that has a small angular definition between the input and output shafts and includes two reduction members that are coaxial with the driven and driving members and that are angularly displaceable with respect to each other.
Many of the prior art devices, such as Pittman and Kaspareck rely upon a pivotal movement of a pin within a slot in order to achieve the relative rotational movement between driven and driving members. Consequently, these devices are subject to a great deal of wear in these particular areas as well as known wear areas such as the intermeshing teeth. Consequently, it would be desirable to have a speed changer of the gear type that did not rely upon the prior art pin/slot type of apparatus for the relative rotational difference between the driven and driving members.